1. Field of the Invention
The present invention relates to a flying head slider having a read-write head that reads or writes data from/into a rotating recording media such as a magnetic disk, and a magnetic disk apparatus equipped with the flying head slider.
2. Description of the Related Art
In magnetic disk apparatuses, a physical space between a flying head slider (hereinafter simply referred to as the “slider”) and a disk is represented generally by two types of amounts: an element flying amount indicating the space between a read-write head and the disk surface and a minimum flying amount indicating a minimum space between the slider and the disk, and the two types of amounts are appropriately used for indicating a magnetic property and a mechanical property, respectively. Note that the slider commonly flies with respect to the disk in the state of having a pitch angle and a roll angle, thereby the element flying amount and the minimum flying amount are different in general.
In order to assure mechanical reliability (that is mainly to avoid a problem caused by a contact of a head with the disk) in the magnetic disk apparatuses, it should be ensured that the above-mentioned minimum flying amount is at a prescribed amount or more. The minimum flying amount lowers due to (1) a flying amount fluctuation caused by a manufacturing error, (2) a flying amount down caused during a head seek time, and (3) a flying amount down caused at the time of a pressure reduction (hereinafter referred to as the “pressure reducing characteristic”, and when the reduction in the flying amount is small, the pressure reducing characteristic is indicated to be good), thereby these factors should be considered to the fullest extent in designing and manufacturing, so that there have been many ingenuities to suppress the flying amount reduction.
The above-described factors that reduce the flying amount are all important for ensuring the reliability of magnetic recording devices, however, recently, magnetic disk apparatuses are increasingly mounted on mobile devices and so forth. Accordingly, in consideration of such a circumstance under which the magnetic disk apparatuses are utilized in more various environments more than before, the improvement in the pressure reducing characteristic, which is an evaluation indicator of reliability, can be said to be the most important factor.
The pressure reducing characteristic, that is, the reduction in the minimum flying amount under the low pressure environment, is caused by a reduction in the flying power generation accompanied by a reduction in atmosphere density under the low pressure environment. Under the low pressure environment, the air density is reduced, so that the pressure allowing the slider to fly is reduced in the case of the same flying posture and space as of the normal pressure. Accordingly, in order to balance a load and the flying power, the flying posture and the flying space are forced to lower to the extent that the same flying power as of the normal pressure can be obtained, and the reduction in the flying space is said to be a reduction in the pressure reducing characteristic.
One of the approaches to suppress the reduction of the pressure reducing characteristic is to increase positive pressure generation at an air outflow edge of the slider, namely at a trailing pad arranged in the vicinity of a read-write element. Along with year-by-year reductions in the flying amount, the positive pressure at the trailing pad can be said to have shown an increase. However, at the same time, the size reduction of the sliders shows a progress, so that the positive pressure increase at the trailing pad is limited in view of the pad area reduction along therewith and the limitation on the load reduction for maintaining a shock resistance.
Meanwhile, by closely watching the flying posture (the pitch angle and roll angle) and the flying space of the slider at the time of the pressure reduction, it is possible to improve the pressure reducing characteristic by positively making use of their fluctuations. The reason will be described below.
First, as for the roll angle, the conventional slider equipped with the read-write element at the lateral center thereof shows no fluctuation in the element flying amount when the roll angle becomes large, while the minimum flying amount shows a reduction. Accordingly, it is required for improving the pressure reducing characteristic to prevent the increase in the roll angle.
Next, as for the pitch angle, generally, a leading pad and the trailing pad have different flying amounts from each other, and the leading pad has a larger flying amount reduction at the time of the pressure reduction, in other words, a reduction in the pitch angle is inevitable in relation thereto. However, when the pitch angle is reduced, then the minimum flying amount increases together (and the same is equally applicable to the element flying amount).
Accordingly, the provision of a positive pressure pad that generates a relatively large pressure between the leading pad and the trailing pad, and the design such that the slider rotates around the center of generating the positive pressure can prevent the minimum flying amount and the element flying amount from being reduced. For the positive pressure pad arranged between the leading pad and the trailing pad in consideration of the suppression of the roll angle, side pads arranged at right and left in the longitudinal direction of the slider can be said to be preferable (see for example Japanese Patent Laid-open Application No. 2002-163815 (Paragraph No. 0047 and so forth)).
As described above, in order to improve the pressure reducing characteristic, it is important to make use of the pitch angle reduction at the time of the pressure reduction, and it is therefore necessary to arrange the side pads generating larger positive pressure between the leading pad and the trailing pad. It should be note that, although the side pads preferably have larger areas and are arranged at the air outflow edge side, the design constraints as will be described below should be considered to the fullest extent.
First, a conventional negative pressure slider has a negative pressure cavity surrounded by the leading pad and the side pads for the purpose of effectively generating negative pressure, and the total amount of the negative pressure generated here is determined substantially by the cavity depth and the area of the negative pressure cavity. Accordingly, in order to generate larger negative pressure for the improvement of the pressure reducing characteristic as well as the shock resistance, the area of the negative pressure cavity is required to be increased, and therefore, preferably, the side pads are laterally narrow as much as possible.
Further, when the negative pressure generated in the negative cavity is increased, the pitch angle is reduced in general, so that the corresponding positive pressure is required to be generated at the leading pad. Backed by this, it is impossible to increase the side pads toward the air inflow side to a large degree so as to ensure a necessary area for the leading pad.
Furthermore, when the side pads are arranged at the air outflow edge side excessively, the space between the air outflow edge of the side pad and the disk surface becomes small, so that the side pad contacts with the disk surface in the case of an accidental fluctuation in the flying amount or the flying posture of the slider, leading to lower the reliability of the apparatus. Accordingly, the arrangement of the side pads at the air outflow edge sides is also limited. Among others, since the side pads are arranged at both the lateral ends of the slider, the side pads tend to contact with the disk surface when the roll angle is increased.
As described above, the side pads preferably generate larger positive pressure as much as possible in view of the pressure reducing characteristic, however, in view of the above-described three design constraints, it is impossible to increase the positive pressure generation by the increase of the area. Accordingly, the positive pressure generation increase per unit area (hereinafter referred to as the “positive pressure generation efficiency”) is necessary.
Thus, with the introduction of the side pad exhibiting higher efficiency in generating positive pressure, the roll moment caused by manufacturing errors can also be suppressed in addition to the improvement in the pressure reducing characteristic, so that the fluctuation in the roll angle caused thereby can be suppressed to a small level. Namely, it is possible to prevent the reduction of the minimum flying amount compared to the element flying amount, leading to the improvement in the reliability of the apparatuses.
Moreover, such a side pad can realize a desired pressure even in a small area, so that it is effectively used for a slider of a smaller size such as a femto slider (width×length×height=0.7×0.85×0.23 [mm]).